Abstract

The materials options to combine high giant magnetoresistance(GMR) ratios with soft magnetic properties have been relatively few, with NiFe providing low-field switching in the great majority of studies. These NiFe layers tend to be hardened appreciably when directly exchange coupled to Co to provide higher GMR ratios, as in (Ta)/NiFe/Co/Cu/Co/NiFe/FeMn spin valves. We propose magnetically soft, amorphous CoZr as a replacement couple to Co in these and other structures. While the high resistivity of amorphous films discourages their use as a single switching element, it favors their use as the drive layer for Co in a spin valve. Our transport simulations, using the Camley–Barnas model modified by Dieny,1 indicate that GMR ratios fall off much less steeply with increasing -CoZr drive layer thickness than with NiFe drive layer thickness. Since lower coercivities are expected for higher fractions of the drive material, CoZr-based spin valves show promise in combining soft properties and high GMR ratios. We have demonstrated the combination of magnetic softness and high GMR ratio in our own CoZr-based spin valves. A free layer coercivity of 7.2 Oe and GMR ratio of 6.4% were achieved in a nominal structure of NiO(400)/Co(50)/Cu(20)/Co(25)/CoZr(200AA). Differential coercivitystructures were deposited as well, using Cr underlayers to induce hardness of the bottom Co. An identical “active layer” structure of the form demonstrates GMR ratios as high as 4.9%; removal of the interfacial Co layer reduces the GMR ratio to 2.8%, in accordance with our expectations. Discussion of optimization and detailed structural analysis will be presented in the full paper.